KR20050041316A - A method for preparing poly(2,5-benzimidazole) - Google Patents

Abstract

The present invention relates to a method for producing a poly (2,5-benzimidazole) that can be used as a polymer electrolyte membrane of a fuel cell, the production method is P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F And a step of polymerizing the 3,4-diaminobenzoic acid monomer using a dehydrating agent containing).

Description

Production method of poly (2,5-benzimidazole) {A METHOD FOR PREPARING POLY (2,5-BENZIMIDAZOLE)}

[Industrial use]

The present invention relates to a method for preparing poly (2,5-benzimidazole), and more particularly, to a method for preparing poly (2,5-benzimidazole) having excellent proton conductivity, and a poly produced according to the method. A fuel cell comprising a (2,5-benzimidazole) polymer electrolyte membrane and a poly (2,5-benzimidazole) polymer electrolyte membrane.

[Prior art]

A fuel cell is an electrochemical cell in which free energy changes due to fuel oxidation are converted into electrical energy. In fuel cells, organic fuels such as methanol, formaldehyde or formic acid are oxidized to carbon dioxide at the anode and air or oxygen is reduced to water at the cathode. In part, fuel cells using organic fuels are extremely attractive, both on installation and portable, because of the high specific energy of organic fuels (eg, the specific energy of methanol is 6232 wh / kg).

In fuel cells, a solid polymer membrane is positioned between an anode and a cathode and serves as a medium for proton movement between two electrodes. BACKGROUND OF THE INVENTION As a conductive solid polymer membrane of a fuel cell, a fluorine-based electrolyte membrane such as Dow or Dupon's perfluorocarbon sulfonic acid membrane (Nafion ^™ ) is widely used because of its excellent chemical stability, high ionic conductivity and excellent mechanical properties.

However, the fluorine-based electrolyte has a disadvantage in that the manufacturing process is complicated and the price is high. In addition, because the heat resistance is high, but the heat resistance limit does not exceed 100 ℃, fluorine-based electrolyte membranes are a low pollution power source for automobiles. When used in fuel cells, small-sized power sources or portable power sources, it is not necessary to cool the reformed gas or remove carbon monoxide from the reformed gas. It has become a factor that complicates the system. In addition, the proton conductivity is low at a high temperature of more than 80 ℃ or a low humidity range of less than 60%, there is a problem showing low methanol cross-over (cross-over).

Therefore, various sulfonated polymers, such as polyimide, polysulfone, polystyrene, polyphenylene and polyether ether ketone (PEEK), have been developed to obtain a polymer electrolyte membrane that can replace the fluorine-based electrolyte membrane. Celanese is a material that can overcome the shortcomings of fluorine-based polymers such as Nafion and poly [2,2 '-(m-phenylene) -5,5'-bibenzimidazole] (polybenzimidazoles, PBI)). PBI has a much lower methanol permeability than Nafion fluorine-based polymers and can be supplied at low cost because it consists of pure hydrocarbons. In addition, since it shows high conductivity at a temperature of 100 ° C. or higher, it can be used in high temperature fuel cells.

Poly (2,5-benzimidazole) has a structure and conductivity similar to that of PBI but can be produced as a polymer electrolyte membrane for fuel cells having better mechanical properties because it can produce a polymer having a high molecular weight. Poly (2,5-benzimidazole) is a 3,4-diaminobenzoic acid using polyphosphoric acid or a mixture of P ₂ O ₅ and phosphoric acid as a dehydrating reagent. It can be synthesized by heating (3,4-diaminobenzoic acid). However, these dehydrating agents are very viscous, so they can only be handled by raising the temperature to 100 ° C. or higher, and they are not easy to handle. In order to use poly (2,5-benzimidazole) as a polymer electrolyte membrane for fuel cells, it is urgently required to develop a new synthesis method that can overcome the disadvantages of synthesis and purification.

The present invention is to solve the above problems, an object of the present invention is to provide a method for producing a poly (2,5-benzimidazole) that can be used as a polymer electrolyte membrane having excellent proton conductivity and low methanol permeability will be.

Another object of the present invention is to provide a poly (2,5-benzimidazole) polymer electrolyte membrane prepared according to the above method and a method for producing the same.

Still another object of the present invention is to provide a fuel cell comprising the poly (2,5-benzimidazole) polymer electrolyte membrane.

In order to achieve the above object, the present invention is P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) It provides a method for producing poly (2,5-benzimidazole) comprising the step of polymerizing a 3,4-diaminobenzoic acid monomer using a dehydrating agent comprising a.

The present invention also provides a poly (2,5-benzimidazole) polymerizing a 3,4-diaminobenzoic acid monomer using a dehydrating agent comprising P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F). It provides a polymer solution comprising a, and provides a method for producing a poly (2,5-benzimidazole) polymer electrolyte membrane comprising the step of casting the polymer solution on a substrate.

The present invention also provides a fuel cell comprising a polymer electrolyte membrane of poly (2,5-benzimidazole) prepared by the above method.

Hereinafter, the present invention will be described in more detail.

In the present invention, poly (2,5-benzimidazole) used as a polymer electrolyte membrane of a fuel cell is prepared using a dehydrating agent containing P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F). As a monomer for synthesizing poly (2,5-benzimidazole), 3,4-diaminobenzoic acid is mixed with the dehydrating agent and heated to allow polymerization. The monomer 3,4-diaminobenzoic acid is preferably used after being purified by reacting with a base or an acid before mixing with a dehydrating agent.

Preferably, the P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) are mixed and used in a uniform solution state.

The dehydrating agent used in the present invention is a transparent solution in which P ₂ O ₅ is completely dissolved in CX ₃ SO ₃ H (X is hydrogen or F). Polyphosphoric acid or a mixture of P ₂ O ₅ and phosphoric acid, which is conventionally used as a dehydrating agent, should be polymerized at a temperature of 200 ° C. or higher for at least 3 hours, but using the dehydrating agent of the present invention, it is about 30 minutes at lower 160 ° C. Degree of polymerization can be carried out.

In addition, since the conventional dehydrating agent has a high viscosity, polymerization proceeds unevenly in a state where it is mixed with the monomer unevenly, and poly (2,5-benzimidazole) as a final product is obtained as a hard lump, which is useful for the recovery and purification of the polymer. It takes time, and in order to prepare it as a polymer electrolyte membrane, a fine grinding process is required. The finely pulverized polymer is made into a powder, chip, or fiber form, and then dissolved in a solvent to prepare an electrolyte membrane. That is, it should be carried out in two stages, the synthesis process of polymer and the film formation process of polymer.

However, when the poly (2,5-benzimidazole) is produced using the dehydrating agent of the present invention, the polymerization proceeds in the state in which the monomer is completely dissolved in the dehydrating agent, and the final product is not a hard mass, but in the form of fine fibers. It can be obtained so that purification can be easily carried out. That is, poly (2,5-benzimidazole) synthesis and the manufacturing process of the electrolyte membrane can be performed in one step (one step) is advantageous because it can save time, energy, etc. in the process.

P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) are preferably used in a weight ratio of 0.5-2: 10.

Synthesized polymers can be obtained by precipitation in non-solvents (solvents that do not dissolve polymers at all). It is preferable to use a mixture of water and ethanol or methanol as the non-solvent.

Phosphoric acid doped in the polymer or present between the polymer chains cannot be easily removed by methods such as reduced pressure. In order to remove the phosphoric acid, it is necessary to grind it into powder, to prepare it in a fiber form, or to use a method of reacting with ammonium hydroxide in a Soxhlet extractor. Most of these operations require a long time and energy, which is a step that must be removed for the commercialization of the electrolyte membrane. In the present invention, since the phosphoric acid is almost removed in the step of precipitating in the non-solvent, it can be carried out by omitting the above process or shortening the process time.

Poly (2,5-benzimidazole) polymer made according to the present invention is represented by the following formula (1).

[Formula 1]

1 is a schematic diagram of a fuel cell 1 comprising an anode 3, a cathode 5, and a polymer electrolyte membrane 7. The anode chamber 9 is filled with a mixture of organic fuel (for example methanol) and water, and the cathode chamber 11 is filled with air and oxygen. The organic fuel circulates through the anode 3 while the oxygen and air are pumped into the cathode chamber 11 and circulated past the cathode 5. Oxidation reaction of organic fuel occurs at the anode 3 and reduction reaction of oxygen occurs at the cathode 5 to generate a voltage difference between the two electrodes. Hydrogen ions or protons produced at the anode 3 pass directly through the electrolyte 7 to the cathode 5. Therefore, the electrolyte membrane should have excellent proton conductivity and low permeability of methanol used as fuel.

Since the poly (2,5-benzimidazole) polymer of the present invention has high proton conductivity and low methanol permeability, it may be usefully used as a polymer electrolyte membrane of a fuel cell.

As described above, the poly (2,5-benzimidazole) polymer of the present invention is obtained in fine fiber form in one step, so that the doped phosphoric acid is easily removed. In addition, using the synthesized polymer can be carried out a film forming process for producing an electrolyte membrane immediately. That is, the synthesized polymer solution is cast on a substrate to prepare a polymer film to prepare an electrolyte membrane. The polymer film cast on the substrate may be soaked in water and separated from the substrate. Casting a thin film can easily remove CH ₃ SO ₃ H and P ₂ P ₅ used as a solvent for polymerization. CX ₃ SO ₃ H present in the polymer film is removed by high pressure and decompression or by non-solvent.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

Example 1 Poly (2,5-benzimidazole) Preparation

1-1 Purification of 3,4-Diaminobenzoic acid

50 g of 3,4-diaminobenzoic acid was dispersed in 500 mL of distilled water and heated to 70 ° C. Hydrazine hydrate was added slowly to obtain a uniform solution. 20 g of activated carbon black was added to the solution and further heated for 30 minutes. Filtration was carried out using Celite while the solution was hot, and acetic acid was slowly added until the crystals formed were cooled to room temperature. The solution was left to stand at room temperature for another day, and the resulting crystals were filtered and dried in a vacuum oven at 70 ° C. for 36 hours. ¹ H-NMR (D ₂ SO ₄ ) δ 8.40-8.15 (m, 2H, Ar H ), 7.62 (d, 1H, Ar H , J ₃ = 8.0 Hz); mp (DSC): 204 ° C. (temperature rise: 0.1 ° C./min).

1.2 Manufacture of dehydrating agent

2 g of P ₂ O ₅ and 20 mL of CH ₃ SO ₃ H were mixed and stirred for 12 hours to obtain a uniform dehydrating solution.

1.3 Synthesis of Poly (2,5-benzimidazole)

2 g of the purified 3,4-diaminobenzoic acid of 1.1 was added to the dehydrating agent solution of 1.2 and heated at 160 ° C. for 30 minutes. The hot polymer solution was slowly poured into a mixed solvent of 300 mL of water and 300 mL of methanol using a peristaltic pump to obtain fine fibers. Phosphoric acid remaining in the ABPBI was removed by using a 10% aqueous ammonium hydroxide solution in a polymer fiber (Soxhlet extractor). ¹ H-NMR (D ₂ SO ₄ ) δ 8.64-7.41 (b, 3H, Ar H ), 5.38 (s, 1H, N- H ); Viscosity 30 ° C., using H ₂ SO ₄ : 4-5 dL / g)

Example 2: Preparation of poly (2,5-benzimidazole) electrolyte membrane

2 g of 3,4-diaminobenzoic acid purified in 1.1 of Example 1 was added to the dehydrating agent solution prepared in 1.2 of Example 1, and heated at 160 ° C. for 30 minutes to conduct polymerization. The polymer solution was poured into a glass plate and a polymer film was cast using a doctor blade. The polymer film was placed in a vacuum oven at 130 ° C. and CH ₃ SO ₃ H was removed for 24 hours. The prepared polymer film was washed with water and ethanol to completely remove CH ₃ SO ₃ H remaining in trace amounts to prepare an electrolyte membrane.

Example 3 Preparation of Poly (2,5-benzimidazole) Electrolyte Membrane

2 g of 3,4-diaminobenzoic acid purified in 1.1 of Example 1 was added to the dehydrating agent solution prepared in 1.2 of Example 1, and heated at 160 ° C. for 30 minutes to conduct polymerization. The polymer solution was poured into a glass plate, a polymer film was cast using a doctor blade, and then immersed in water to drop the polymer film from the glass plate. The polymer film was placed in a vacuum oven at 130 ° C. and CH ₃ SO ₃ H was removed for 24 hours. The prepared polymer film was washed with water and ethanol to completely remove the residual CH ₃ SO ₃ H.

In the present invention, by using P ₂ O ₅ CX ₃ SO ₃ H (X is hydrogen or F) as a dehydrating agent, the monomer is completely dissolved in the dehydrating agent to proceed the polymerization in a uniform mixing system, the final product is also a fine fiber (fiber Purification can be easily carried out in the form of), and since the electrolyte membrane for the fuel cell can be prepared in-situ immediately after the polymerization is completed, it is advantageous to reduce the time and energy in the process.

Poly (2,5-benzimidazole) prepared according to the present invention has a high proton conductivity and low methanol permeability, and thus may be usefully used as a polymer electrolyte membrane of a fuel cell.

1 is a schematic diagram of a fuel cell including a polymer electrolyte membrane.

<Description of the symbols for the main parts of the drawings>

1: fuel cell 3: anode

5: cathode 7: electrolyte membrane

9: anode chamber 11: cathode chamber

Claims (10)

Poly (2,5-benzimidazole) comprising the step of polymerizing a 3,4-diaminobenzoic acid monomer using a dehydrating agent comprising P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F). Manufacturing method. The method for preparing poly (2,5-benzimidazole) according to claim 1, wherein the monomer 3,4-diaminobenzoic acid is purified by reaction with a base or an acid before mixing with a dehydrating agent. The poly (2,5-benzimidazole) according to claim 1, wherein P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) are mixed and used in a weight ratio of 0.5-2: 10. Manufacturing method. The method of claim 1, further comprising the step of precipitating the poly (2,5-benzimidazole) in a non-solvent to obtain a polymer in a fine fiber form. Poly (2,5-benzimidazole) prepared according to any one of claims 1 to 4. Polymer solution containing poly (2,5-benzimidazole) by polymerizing 3,4-diaminobenzoic acid monomer using a dehydrating agent containing P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) Manufacturing the A method for producing a poly (2,5-benzimidazole) polymer electrolyte membrane comprising the step of casting the polymer solution on a substrate. The method for preparing a poly (2,5-benzimidazole) polymer electrolyte membrane according to claim 6, wherein the monomer 3,4-diaminobenzoic acid is purified by reacting with a base or an acid before mixing with a dehydrating agent. The poly (2,5-benzimidazole) polymer of claim 6, wherein P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F) are mixed and used in a weight ratio of 0.5-2: 10. Method for producing an electrolyte membrane. A poly (2,5-benzimidazole) polymer electrolyte membrane prepared according to any one of claims 6 to 8. A fuel cell comprising the poly (2,5-benzimidazole) polymer electrolyte membrane of claim 9.